A liquid crystal panel includes a liquid crystal layer interposed between two substrates and is used in combination with polarizing plates as a display for a television set or a personal computer, or as a light valve for a projection-type display apparatus (liquid crystal projector).
Important performances required of these display apparatuses include transmissivity (brightness) and contrast (white/black illumination rate). High transmissivity provides bright images and, for projectors, reduces electric power consumption of a light source, such as an LED, a fluorescent lamp, or an UHP lamp, at the same time. In addition, high contrast provides high-definition images.
However, in the liquid crystal display apparatus using the above-described liquid crystal panel, a phase difference at the liquid crystal layer serves as one of the causes of reduction in contrast. More specifically, although linearly polarized light incident on the liquid crystal layer is ideally emitted as linearly polarized light, elliptically polarized light is emitted in practice because orientations of liquid crystal molecules near substrate interfaces do not change even when a voltage is applied. In addition, incident light with a polar angle is not transmitted along an optical axis of the liquid crystal molecules, and therefore is also emitted as elliptically polarized light. Then, when the elliptically polarized light is emitted from the liquid crystal panel, so-called light leakage occurs in which light passes through the polarizing plate at the emission side during black display. This leads to degradation of contrast.
Accordingly, in the liquid crystal display apparatus, an optical compensation layer for compensating for the optical phase difference generated at the liquid crystal layer is provided, thereby achieving a black level display without light leakage. Such an optical compensation layer includes, for example, a film of liquid crystal material oriented in a predetermined state. In addition, in a liquid crystal panel portion of, for example, a liquid crystal projector, an incident-side polarizing plate, a liquid crystal panel, a single-layer or a double-layer optical compensation layer (optical compensation element), and an emission-side polarizing plate are arranged in that order from a light incident side. In this state, the optical compensation layer may be disposed in a state such that the optical compensation layer is in tight contact with the liquid crystal panel (for the above, refer to Japanese Unexamined Patent Application Publication No. 2002-14345 (paragraphs 29-30 and 46)).
However, in the liquid crystal display apparatus having the above-described structure, the optical compensation layer is disposed in such a state that the optical compensation layer is exposed to the atmosphere. Therefore, there is a problem that the optical compensation layer is easily degraded due to supply of oxygen and moisture. In particular, in the projection-type liquid crystal display apparatus, since the liquid crystal panel is irradiated with strong light, the optical compensation layer made of an organic material, such as the above-described film of liquid crystal material, is severely damaged due to the presence of oxygen and moisture, and is required to have light resistance.
Therefore, it is an object of the present invention to provide a liquid crystal display apparatus which includes an optical compensation layer in addition to a liquid crystal panel and which is capable of preventing degradation of the optical compensation layer, thereby providing high long-term reliability in display characteristics.